Skin cancer is one of the most common cancers in the United States, and it is also one of the most preventable. Preventive behaviors include reducing peak sun exposure, wearing sunscreen, seeking shade, wearing protective clothing, and avoiding sunburn. Few skin cancer prevention programs in outdoor settings have been evaluated in controlled trials, and as with many preventive interventions, little is known about how to successfully disseminate those that are found efficacious. The efficacy of the Pool Cool program in aquatic settings (swimming pools) was demonstrated in a previous trial, and a Dissemination Pilot Study with 186 swimming pools was completed. The aims of this study are to evaluate the effects of two strategies for diffusion of the Pool Cool skin cancer prevention program on: program implementation, maintenance, and sustainability; organizational and environmental supports for sun protection; and sun protection habits and sunbums among children. Ancillary aims are to examine predictors of diffusion, examine the mediating role of lifeguards and aquatic instructors; characterize correlates of participation in a diffusion trial and rates of spontaneous diffusion; and investigate longitudinal patterns of sun protection behaviors over multiple years. The study will use a three-level nested experimental design; the three levels are Field Coordinators, swimming pools, and children ages 5 to 10 years in swimming lessons. 32 Field Coordinators will be randomized into Basic and Enhanced (reinforcement + feedback) diffusion conditions. Intervention materials for the children, and strategies for the Field Coordinators, are based principally on Social Cognitive Theory and Diffusion of Innovations. Each Field Coordinator will work with 10 pools for three years (n=320 pools final sample). A sample of 20 parents per pool will be surveyed about their children at baseline and at the end of each summer (n= 6,400 final sample); a cohort sub-sample will be followed over multiple years. The main outcomes of interest will be pool level diffusion endpoints, organizational/environmental change at pools, and child sun protection habits and sunburns. Process evaluation will supplement outcome data. The results of this research will increase our knowledge of the diffusion of evidence-based cancer prevention programs in community settings, and of their long term maintenance and sustainability. The findings will make a significant contribution to our understanding of skin cancer prevention behaviors of individuals and aquatics organizations.